1. Field of the Invention
The present invention relates to a recording apparatus of the toner image transfer type, namely electrostatographic apparatus, such as an electrophotographic apparatus or an electrostatic electrographic apparatus. In particular, it relates to an improved cleaning device to remove residual contaminants from the surface of the recording medium of the recording apparatus after a toner image transfer operation.
2. Description of the Related Art
As is well known, in a recording apparatus of the toner image transfer type, such as an electrophotographic printer or copying machine, or an electrographic printing machine or copying machine, an electrostatic latent image is formed on a recording medium such as a photoconductive drum or dielectric drum. The latent image is developed as a toner image formed on the surface of the drum. Thereafter, the toner image is adhesively transferred onto a printing medium such as cut sheet or web at an image transfer station of the apparatus where the surface of the recording medium and that of the printing medium are set in contact with each other. The present invention is applicable to both electrophotographic recording apparatus and electrographic recording apparatus. However, for clarity and simplicity of description, the description of the present invention will be limited to an electrophotographic recording apparatus having a photoconductive drum and employing cut sheet as a printing medium.
Since the image transfer usually does not remove all the toner particles from the surface of the recording medium but leaves a small amount of toner particles thereon, and since it is necessary to keep the surface of the recording medium clean for subsequent image formation thereon, the surface must be cleaned completely immediately after the image transfer. Accordingly, at the next cleaning station, contaminants remaining on the surface of the photoconductive drum, including residual toner particles, toner carriers, and paper lints, are removed. A cleaning device, therefore, is disposed downstream from the image transfer station with respect to the rotation of the drum. Hereinafter, the terms "downstream" and "upstream" are used with respect to the rotating movement of the photoconductive drum.
There have been two types of conventional cleaning devices. One is a type having a rotatable cleaning means such as a rotatable brush including a number of bristles made of plastic wire, mounted around a rotatable shaft, or a rotatable cylinder of sponge-like material formed around a shaft. The cleaning means extends in the axial direction of the photoconductive drum. The other is a blade type using a blade of elastic material such as polyurethane rubber. The blade extends in the axial direction of the photoconductive drum, and is disposed such that the edge of the blade engages with the rotating surface of the photoconductive drum in pressure contact therewith. The cleaning capability of a cleaning device of the rotatable type is not sufficient since there is a tendency to cause a contaminated toner image on a cut sheet or to cause fluctuated electric discharge of the electric discharger due to the residual toner particles scattered by brushing.
A cleaning device of the blade type normally can clean the surface of the photoconductive drum satisfactorily. However, there is a problem of abrasion of the edge of the blade caused by contaminants of large size such as toner carriers and paper lints accumulated on the edge as described hereafter.
When the feed passage of the cut sheet is selectively disposed in an upper portion of the recording apparatus, the image transfer station must be set at the top portion of the photoconductive drum. This configuration of the arrangement of the photoconductive drum to the printing medium is essentially beneficial for an operator of the apparatus, because removal of jammed sheets and replacement of the photoconductive drum, can be performed very easily and safely from the top side of the apparatus without damaging the surface of the photoconductive drum. The sheet jamming tends to occur at a portion of the sheet feed passage located in the vicinity of the image transfer station. Consequently, approach to the jammed cut sheet and the photoconductive drum by the operator, can be done easily only by opening the upper portion of the recording apparatus.
With respect to the above-described configuration of the arrangement of the photoconductive drum and the feed passage for the cut sheet, the blade must be naturally disposed such that the edge of the blade engages along a substantially downwardly moving surface of the photoconductive drum in pressure contact therewith and the edge of the blade is directly upstream, usually upwardly. When the edge scrapes the surface of the photoconductive drum to remove the contaminants thereon, the scraped contaminants might accumulate on the edge of the blade. The accumulated contaminants contain toner particles, toner carriers and paper lints. The toner particles are fine particles having a diameter of micron order. The toner carriers contained in two-component developer material have diameters of ten micron order. When two-component developer material is employed, the toner carrier tends to be scattered inside the apparatus by the centrifugal force of a rotating magnetic brush which is formed of the developer material. The paper lints have a larger size, range from 50 to 100 microns, and are generated by friction between the advancing printing medium and the sheet feed passages, particularly between the side edge of the printing medium and the passages.
The accumulated contaminants tend to stick to the edge of the blade, forming a layer stuck to a leading surface portion of the blade which is directly in contact with the surface of the photoconductive drum. As a result, the surface of the photoconductive drum is scratched and damaged by the toner carriers and the paper lints after some duration of recording operation. To avoid this damage, the used blades must be replaced with new ones, thus increasing the operating expense.
In addition, friction between an abraded blade edge and the surface of the photoconductive drum causes heat by which toner particles are melted. The melted toner particles make a thin film of toner particles stuck to the surface of the drum, disabling the portion of the surface covered by the film. This phenomenon is referred to in the art as "filming".
In contrast, fine toner particles appear to have a lubricant function. Thus, a layer of toner particles having a thickness is allowed to accumulate on the edge of the blade. However, particularly in a case where the top surface of the blade is formed to be perpendicular to the surface of the drum, forming a step there, toner particles accumulate on the step excessively, forming a pile on the top surface of the blade and the portion of the surface of the drum adjacent to the cleaning edge. This is not desirable because such piled toner particles tend to scatter within the recording apparatus, causing various problems. Further, some toner particles may pass underneath the cleaning edge, leaving a film on the peripheral surface of the drum. The film of toner particles may produce an unclear toner image formation.
As one of the countermeasures to solve the above-described problem in prior art recording apparatus, the edge of the blade is sharpened to be formed in a wedge-like shape, providing the blade with a slanted top surface over which scraped toner particles can easily fall down and the accumulation of the contaminants on the edge is reduced. However, the sharpening of the edge is rather difficult and costly, and the edge tends to be easily abraded by repeated recording operations.